The chemical conversion coating of aluminum and its alloys, iron and its alloys, zinc and its alloys and zinc coated iron alloys is known in the art as a process whereby the surface of the metal is chemically converted to a surface that will more easily accept applied coatings, i.e. paint, and increases the corrosion resistance of the metal. The corrosion resistance aspect of the art is of particular importance in the aircraft industry as they frequently employ aluminum alloys that are easily corroded.
An accepted process involves the use of chromates or dichromates in conjunction with polyvinyl alcohol (see: Kirk-Othmer: Encyclopedia of Chemical Technology, volume 23, Third edition, Pages; 848–865) to generate in-situ a new polymer which consist of a network of various carbon to oxygen to chromium to oxygen to substrate metal bonds. As these are rather toxic, and have a considerable environmental concern, the chromate based conversion coatings are being displaced by less toxic materials. Alternative conversion coatings in current use which may be used are based upon potassium permanganate or zirconium compounds, either by themselves or incorporated in a polymer network.